1. Field of the Invention
The present invention relates to novel composite materials comprising a reinforced glass-ceramic (hereafter "vitroceramic") matrix, and to a process for the production thereof.
2. Description of the Prior Art
Composite materials comprising a vitroceramic matrix and, in particular, a reinforcing amount of fibers, are currently of great technical interest in light of their good thermomechanical properties For this reason, they may advantageously be used in the aeronautical and aerospace fields for applications requiring good strength at intermediate temperatures, i.e., on the order of 600.degree. to 1,000.degree. C.
However, most of the materials of this type developed to date are not completely satisfactory, both relative to their final properties and to the processing thereof.
Among the most widely used and best performing composite materials comprising vitroceramic matrices are those having a matrix which is based on lithium. But matrices of this type display a resistance to corrosion that is not entirely satisfactory.
The technique most typically employed for the production of such materials entails impregnating a fiber preform (reinforcing agent) with a slip containing, in various forms, all of the constituents required to provide the desired vitreous composition, then drying the thus impregnated preform.
The stages of impregnating and drying may be repeated until a prepreg is obtained having the desired amount by volume of fibrous reinforcement and/or a plurality of prepregs is stacked into an array and made integral by heating the dried prepregs at moderate temperatures in order to produce large size mono- or bidirectionally reinforced composites. Finally, the preform is densified in a compression stage at elevated temperatures. This latter stage, having in particular the purpose of making the glass flow through the strands of the preform, requires a relatively low viscosity of the glass (less than 10.sup.7 poises) and thus a high compression temperature.
Hence, to obtain suitable results relative to density and thermomechanical properties, it is known that glasses based on lithium must be compressed at temperatures of at least about 1,300.degree. to 1,400.degree. C. These high pressing temperatures entail the risk of damaging the fibers which constitute the reinforcing structure.